Covert drug abuse has been demonstrated to be a common problem among hospitalized adolescent and young adult psychiatric patients. Moreover abuse of such drugs has been shown to be associated with distinctive alterations in the scalp electroencephalogram. This project is designed to pursue findings of preliminary studies with repeated EEG and psychiatric, neurologic, and neuropsychological evaluations of confirmed drug abusers and controls. A total population within the ages of 12 to 30 years will be examined and selected individuals from the cohort will be evaluated intensively and serially. The goals of such research are to establish the kinds of alterations in intellectual capacity, perception, brain function, and clinical symptoms that differentiate the drug user from psychiatric patients without such problems and to assess the short term course of such manifestations. A further goal of this work is to evaluate the contribution of covert abuse of drugs to clinical diagnosis, treatment, and prognosis.